Irrlicht Engine

I found a website to download some modded Quake 3 levels. Once I load the pk3 file how can I determine the name of the bsp file?

unzip the pk3 file.

Maybe you mean this:
the Q3 file should be nothing else but a zip archiv...
simple rename it to .zip, and unzip it...

Thanks a lot, that is exactly what I was looking for.

Edit:
After trying it out I see these levels must depend on some textures already in the game. Only bits and pieces render

Yes, modding packs always require the original media.
And renaming the app is only required for mouse-only users, the command line tools usually accept all extensions (at least mine do)